I'd say that MTG's initial success was caused by:
A BRILLIANT idea of deckbuilding game, that allowed and even encouraged players to be creative,
And a BRILLIANT flavor of a fantasy world, where the main conflict was between not factions but philosophies (yes I know those were underdeveloped at the moment, but still.)
DESPITE a very poor design, where the usefulness of half of the cards depended entirely on opponent's deck and things like "Counterspell absolutely outclassing Spell Blast" and a lot of rares being ridiculously OP, and a lot of commons being unplayable, and color imbalance.
EDIT: and no, the core system wasn't (ISN'T !!) very good either - basically every MTG clone wants to get rid of or change the land system - cause it's baaad.

As far as an article I've read goes, Richard Garfield designed a boardgame as a hobby for several months, and eventually came with it to a small company of enthusiasts called Wizards of the Coast.
Where he was told by Peter Adikson and co. that his game isn't going to work. And some advice for things.
And he was like - "be right back !"
And in a short time (they haven't exactly explained what they mean by "short", but from some another article - it was one day.) , came with a completely other game - first prototype of magic - that was immediately liked by most of the people there. Yes, there was testing, card creation, polishing, etc - but core concepts were coined by one person in a matter of days, with advice of one another person - Peter Adikson (?).

And that's why FarmVille and it's clones absolutely, deeply s..ks, right ?
Can't say anything about Call of Duty - I am too much of a slowpoke to play shooters.

Overwatch, Dota 2 and Zelda are all AAA games. I don't play any of them, but my impression of them are favorable.

I like playing MMORPGs, but I'm gonna remain skeptical.

I also wonder if I can be a healer, but still Blue-aligned. I don't quite like White or Green's aesthetics.

ESO is also a Triple A game and seems to be doing well

We don't know anything about the actual mechanics of the MMO. It could have card-based combat for all we know.

Personally, I'm unlikely to abandon Guild Wars 2 for whatever MMO Hasbro cooks up, but I'll give it a look if it has enough fashion options for the discerning spellslinger. Because as everyone knows, cosmetics are the real endgame.

It's true. Ragnarok Online was (and in some places still is) the best hat collection simulator ever made.

Cosmetics are not the end-game, the are the game period.